A shear wall is a wall that typically includes braced sheathing panels (also known as shear panels) nailed to framing members and an associated set of hold-downs. The shear wall counters the effects of lateral loads. When building a shear wall, structural plywood or particle-board sheathing panels are typically applied to cover wood stud framing. A nail gun is then typically used to nail the panels to the underlying framing in a specified nailing pattern. The particular pattern is important and is specified by a structural engineer.
One of several methods may be used to construct a shear wall in the field. In one method, the appropriate lengthwise (vertical) spacings between nails are measured and the nail locations are manually marked with a pencil. The marks on the sheathing are then used to place nails during the nailing operation. The manual pencil marking is time consuming. Moreover, the nails are to be properly spaced in not just one dimension (the lengthwise or vertical dimension), but rather are also to be properly spaced offset from the edge of the sheathing (the horizontal dimension). Typically the nails are specified to be spaced a certain distance from the edges of the sheathing panels or from edges of the underlying framing members, depending on the nailing pattern and nailing density specified. Sometimes a chalk line is used to accomplish this horizontal marking. Often, however, the extra trouble of using a chalk line is dispensed with and the horizontal spacing of the nails is just “eyeballed”. Due to this eyeballing, the horizontal spacing of the nails may be irregular and imprecise.
In a second method, no marking whatsoever is performed. The individual with the nail gun simply “eyeballs” both the vertical and horizontal placement of each nail at the time of nailing and then drives the nail using the nail gun. The resulting spacing of nails is therefore not always precise. The person doing the nailing may intend to place nails with a specified three inch vertical spacing, but when the spacing between the actual nails as placed is measured, the spacing may be four inches in places.